Accompanying the proliferation of optical communications using optic fiber cables and laser processors for precision processing in recent years, various types of lasers used as their light sources are expected to have increasingly higher outputs in the future. Along with this trend, response to stabilization of these light sources and prevention of their destruction are becoming increasingly important. Optical isolators are used as devices responsible for the stabilization of the light sources and prevention of their destruction.
Optical isolators are equipped with a Faraday rotator that rotates the polarization plane of incident light in response to application of a magnetic field. Yttrium iron garnet has conventionally been used as Faraday rotators for optical communication applications. However, yttrium iron garnet has the shortcomings of being susceptible to deterioration of thin film single crystal due to increased output of the light source, as well as restrictions on the wavelength bands in which it can be used due to its narrow bandwidth in which light is transmitted. In view of these circumstances, a terbium aluminum garnet single crystal has been developed that demonstrates high optical transmittance over a broad wavelength range of 400 nm to 1500 nm while also demonstrating a large Faraday rotation angle (Patent Document 1), and this single crystal is expected to be used as a Faraday rotator for optical isolators. This single crystal is represented by the general formula indicated below:(Tb3-xScx)Sc2Al3O12 (0.1≦x<0.3).